Also written 枝輪. A short, curved, non-supporting member that forms a diagonal transition between two parallel horizontal beams; a purlin *keta 桁, and a bracket tie beam *tōshihijiki 通肘木, or between two bracket tie beams set at slightly different levels. Shirin may be straight, convex or concave. When used around an interior ceiling, the shirin are either straight or concave and are often considered part of the ceiling. When used on the exterior under the eaves of a building, the shirin are convex. They form a neat transition between the beams, and fill a space that would otherwise be an ugly gap that reveals rough structural members.
The basic type of shirin is called honshirin 本支輪 or *jabara shirin 蛇腹支輪. The latter means shirin that give the impression of being a cornice. It is composed of equally spaced ribs, shirinko 支輪子 or ribs grouped in twos or threes, with the spaces between filled by thin boards called shirin-ita 支輪板. A common name for any style of shirin placed under the eaves is *noki shirin 軒支輪. The ribs are either square or rectangular in section. Some have a slight curve at the top. An example of this type is found in Hōryūji *Kondō 法隆寺金堂 (rebuilt 693), Nara. An example, of straight, slanting shirin is found in Tōshōdaiji *Kōdō 唐招提寺講堂 (8th century) Nara. However, shirin used from the late 7th through the 8th century usually have a gentle curve overall. When stepped bracket complexes are used, a shallow ceiling *nokitenjō 軒天井, and shirin are needed to fill the distance between the purlins and eave ends *nokisaki 軒先.
During the Heian period, the slant of the shirin, both inside the building and outside beneath the eaves, was generally much more abrupt than in previous centuries. On the interior, the upper part of the shirin curves slightly while on the exterior, the lower part has a little curvature and the upper part is straight. One exception are shirin found in Byōdōin *Hōōdō 平等院鳳凰堂 (1053), Kyoto. From the 13th century, Zen style *zenshūyō 禅宗様 shirin became elaborate. *Hishi shirin 菱支輪, have lozenge shape ribs with a curved board backing or a lozenge pattern carved into the surface of the curved boards.
There are many other types of shirin: Nami shirin 波支輪 (constructed in wave pattern), *kumo shirin 雲支輪 (constructed in a cloud pattern), uzumaki shirin 渦巻支輪 (constructed in a spiral pattern), wachigai shirin 輪違支輪 (constructed in a pattern of intersecting circles). Ita shirin 板支輪 are flat boards which provide the backing for the patterns mentioned above. Coved ceilings *oriage tenjō 折上天井 are raised by an arrangement of coved ribs called oriage shirin 折上支輪 that spring from the wall plate *daiwa 台輪 and are attached to the ceiling framing joists *gōtenjō 格天井.
